I am managing 2 offices in the same city but both running with different domains and exchange setup.But i have site to site VPN configured and inter connected.Currently we are using AmazoneSMS (SMTP Gateway service) to route emails to external domains.Is it possible to Send & receive emails from Site A to Site B direct to the exchange servers instead of routing through SMTP gateway.

Hello

on both exch server create send connector with specified domain name, enable verbose logging and test.